JOINT VENTURES AND PARTNERSHIPS - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financial information relating to unconsolidated joint ventures operations
Operating income/(loss)	$ (5,055)	$ 31,257	$ 52,234
Joint Ventures and Partnerships
Financial information relating to unconsolidated joint ventures operations
Total revenues	287,083	267,116	242,630
Property operating expenses	112,347	103,969	91,204
Real estate depreciation and amortization	115,211	106,805	90,037
Gain (loss) on sale of real estate		71,590
Operating income/(loss)	59,525	127,932	61,389
Interest expense	(87,363)	(78,829)	(69,967)
Income/(loss) from discontinued operations			33,826
Other income/(loss)	148
Net (income)/loss attributable to noncontrolling interest		439	(62)
Net income /(loss)	(27,690)	48,664	25,310
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	3,167,984	3,185,185
Cash and cash equivalents	39,405	33,712
Other assets	29,819	23,185
Total assets	3,237,208	3,242,082
Third party debt, net	2,114,420	2,005,566
Accounts payable and accrued liabilities	59,717	83,245
Total liabilities	2,174,137	2,088,811
Total equity	1,063,071	1,153,271
Unconsolidated Joint Venture Other MetLife
Financial information relating to unconsolidated joint ventures operations
Total revenues	61,967	48,032	18,090
Property operating expenses	21,998	21,908	11,655
Real estate depreciation and amortization	35,437	32,625	16,353
Operating income/(loss)	4,532	(6,501)	(9,918)
Interest expense	(17,408)	(13,894)	(6,164)
Net income /(loss)	(12,876)	(20,395)	(16,082)
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	653,729	687,492
Cash and cash equivalents	8,242	8,596
Other assets	4,904	4,290
Total assets	666,875	700,378
Third party debt, net	454,647	443,147
Accounts payable and accrued liabilities	9,753	15,003
Total liabilities	464,400	458,150
Total equity	202,475	242,228
Unconsolidated Joint Venture Vitruvian Park
Financial information relating to unconsolidated joint ventures operations
Total revenues	26,096	23,025	22,916
Property operating expenses	13,732	11,839	11,730
Real estate depreciation and amortization	9,495	7,169	6,835
Operating income/(loss)	2,869	4,017	4,351
Interest expense	(6,051)	(5,030)	(5,095)
Net income /(loss)	(3,182)	(1,013)	(744)
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	315,541	299,420
Cash and cash equivalents	8,865	7,612
Other assets	2,241	1,972
Total assets	326,647	309,004
Third party debt, net	162,131	131,281
Accounts payable and accrued liabilities	14,968	16,931
Total liabilities	177,099	148,212
Total equity	149,548	160,792
Unconsolidated Joint Venture UDR Met Life I Partnership
Financial information relating to unconsolidated joint ventures operations
Total revenues	3,187		278
Property operating expenses	3,066	93	552
Real estate depreciation and amortization	3,392		52
Gain (loss) on sale of real estate		(17)
Operating income/(loss)	(3,271)	(110)	(326)
Interest expense	(1,872)
Income/(loss) from discontinued operations			(375)
Net income /(loss)	(5,143)	(110)	(701)
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	124,112	108,958
Cash and cash equivalents	698	514
Other assets	1,074	2
Total assets	125,884	109,474
Third party debt, net	70,833	30,555
Accounts payable and accrued liabilities	1,935	12,700
Total liabilities	72,768	43,255
Total equity	53,116	66,219
Unconsolidated Joint Venture UDR MetLife II Partnership
Financial information relating to unconsolidated joint ventures operations
Total revenues	158,738	156,920	169,175
Property operating expenses	56,403	52,450	52,322
Real estate depreciation and amortization	44,721	45,144	46,135
Gain (loss) on sale of real estate		(609)
Operating income/(loss)	57,614	58,717	70,718
Interest expense	(49,118)	(50,603)	(51,173)
Income/(loss) from discontinued operations			34,201
Net income /(loss)	8,496	8,114	53,746
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	1,609,903	1,641,338
Cash and cash equivalents	11,192	11,947
Other assets	18,670	15,037
Total assets	1,639,765	1,668,322
Third party debt, net	1,089,231	1,108,156
Accounts payable and accrued liabilities	21,258	19,477
Total liabilities	1,110,489	1,127,633
Total equity	529,276	540,689
Unconsolidated Joint Venture Three Washington DC
Financial information relating to unconsolidated joint ventures operations
Total revenues	20,703	20,327	19,997
Property operating expenses	8,318	8,159	7,828
Real estate depreciation and amortization	14,487	14,480	14,444
Operating income/(loss)	(2,102)	(2,312)	(2,275)
Interest expense	(6,739)	(5,264)	(5,369)
Net income /(loss)	(8,841)	(7,576)	(7,644)
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	182,970	195,625
Cash and cash equivalents	1,794	829
Other assets	1,320	905
Total assets	186,084	197,359
Third party debt, net	165,699	165,801
Accounts payable and accrued liabilities	1,860	1,745
Total liabilities	167,559	167,546
Total equity	18,525	29,813
Preferred Equity Investment West Coast Development JV
Financial information relating to unconsolidated joint ventures operations
Total revenues	16,392	18,812	12,174
Property operating expenses	8,830	9,520	7,117
Real estate depreciation and amortization	7,679	7,387	6,218
Gain (loss) on sale of real estate		72,216
Operating income/(loss)	(117)	74,121	(1,161)
Interest expense	(6,175)	(4,038)	(2,166)
Other income/(loss)	148
Net (income)/loss attributable to noncontrolling interest		439	(62)
Net income /(loss)	(6,144)	69,644	(3,265)
Combined summary of balance sheets relating to unconsolidated joint ventures
Total real estate, net	281,729	252,352
Cash and cash equivalents	8,614	4,214
Other assets	1,610	979
Total assets	291,953	257,545
Third party debt, net	171,879	126,626
Accounts payable and accrued liabilities	9,943	17,389
Total liabilities	181,822	144,015
Total equity	110,131	113,530
Developer Capital Program excluding West Coast Development Joint Ventures
Financial information relating to unconsolidated joint ventures operations
Total revenues	6,000	7,800	8,500
Expenses	1,800	9,500	$ 12,200
Combined summary of balance sheets relating to unconsolidated joint ventures
Total assets	248,100	79,100
Total liabilities	22,500	800
Total equity	$ 225,600	$ 78,300